package runtimeconfig

import (
	"fmt"
	"os"
	"path"
	"time"

	"github.com/itworx/pulse/internal/config"
)

const (
	defaultAgentID              = "pulse-agent"
	defaultCollectInterval      = 10 * time.Second
	minimumCollectInterval      = time.Second
	maximumCollectInterval      = 5 * time.Minute
	defaultProcRoot             = "/proc"
	defaultSysRoot              = "/sys"
	maximumAgentIDLength        = 120
	maximumHostNameLength       = 255
	maximumConfigurableRowCount = 5000
)

// AgentConfig is everything pulse-agent needs to run. It is deliberately separate from
// internal/config: the agent container receives only PULSE_DATABASE_URL and its own
// settings, and must not require the public URL, OIDC or Prometheus configuration the
// API validates.
type AgentConfig struct {
	Service ServiceConfig
	// AgentID identifies this agent in every snapshot and in the protocol hello.
	AgentID string
	// DatabaseURL is the only credential the agent holds; it is never logged.
	DatabaseURL string
	// CollectInterval is how often a full collection pass runs. The scheduling loop
	// itself ticks faster when this is large, so the heartbeat stays inside the
	// 10 second window the healthcheck contract requires.
	CollectInterval time.Duration
	// ProcRoot and SysRoot are the read-only mounts the collector reads.
	ProcRoot string
	SysRoot  string
	// FilesystemRoot prefixes mount points before statfs. Empty disables filesystem
	// capacity collection, which is the safe default in a container where the host's
	// mount points do not resolve.
	FilesystemRoot string
	// HostName overrides the name read from the reader's UTS namespace, which in a
	// container is the container's name rather than the host's.
	HostName string
	// MaxProcesses bounds the process inventory; zero uses the domain default.
	MaxProcesses int
	// UnraidURL and UnraidAPIToken are an optional, read-only source for bounded
	// container snapshots. They must be configured together; the token is never logged.
	UnraidURL      string
	UnraidAPIToken string
	// UnraidCAFile optionally adds one private CA/leaf certificate while retaining
	// normal TLS hostname and chain verification.
	UnraidCAFile string
}

// LoadAgent reads and validates the agent's environment.
func LoadAgent() (AgentConfig, error) {
	service, err := Load("agent")
	if err != nil {
		return AgentConfig{}, err
	}
	agent := AgentConfig{
		Service:        service,
		AgentID:        valueOrDefault("PULSE_AGENT_ID", defaultAgentID),
		DatabaseURL:    os.Getenv("PULSE_DATABASE_URL"),
		ProcRoot:       valueOrDefault("PULSE_AGENT_PROC_ROOT", defaultProcRoot),
		SysRoot:        valueOrDefault("PULSE_AGENT_SYS_ROOT", defaultSysRoot),
		FilesystemRoot: os.Getenv("PULSE_AGENT_FS_ROOT"),
		HostName:       os.Getenv("PULSE_AGENT_HOST_NAME"),
		UnraidURL:      os.Getenv("PULSE_UNRAID_URL"),
		UnraidAPIToken: os.Getenv("PULSE_UNRAID_API_TOKEN"),
		UnraidCAFile:   os.Getenv("PULSE_UNRAID_CA_FILE"),
	}
	if len(agent.AgentID) > maximumAgentIDLength {
		return AgentConfig{}, fmt.Errorf("PULSE_AGENT_ID must be at most %d characters", maximumAgentIDLength)
	}
	if agent.DatabaseURL == "" {
		return AgentConfig{}, fmt.Errorf("PULSE_DATABASE_URL is required: the agent publishes snapshots through the database")
	}
	if err := config.ValidateDatabaseURL(agent.DatabaseURL); err != nil {
		return AgentConfig{}, err
	}
	interval, err := durationOrDefault("PULSE_AGENT_COLLECT_INTERVAL", defaultCollectInterval, minimumCollectInterval, maximumCollectInterval)
	if err != nil {
		return AgentConfig{}, err
	}
	agent.CollectInterval = interval
	for name, value := range map[string]string{
		"PULSE_AGENT_PROC_ROOT": agent.ProcRoot,
		"PULSE_AGENT_SYS_ROOT":  agent.SysRoot,
	} {
		if !path.IsAbs(value) {
			return AgentConfig{}, fmt.Errorf("%s must be an absolute path", name)
		}
	}
	if agent.FilesystemRoot != "" && !path.IsAbs(agent.FilesystemRoot) {
		return AgentConfig{}, fmt.Errorf("PULSE_AGENT_FS_ROOT must be an absolute path when set")
	}
	if len(agent.HostName) > maximumHostNameLength {
		return AgentConfig{}, fmt.Errorf("PULSE_AGENT_HOST_NAME must be at most %d characters", maximumHostNameLength)
	}
	if (agent.UnraidURL == "") != (agent.UnraidAPIToken == "") {
		return AgentConfig{}, fmt.Errorf("PULSE_UNRAID_URL and PULSE_UNRAID_API_TOKEN must be configured together")
	}
	if agent.UnraidURL != "" {
		if err := config.ValidateURL(agent.UnraidURL, true); err != nil {
			return AgentConfig{}, fmt.Errorf("PULSE_UNRAID_URL: %w", err)
		}
	}
	if agent.UnraidCAFile != "" {
		if agent.UnraidURL == "" || !path.IsAbs(agent.UnraidCAFile) {
			return AgentConfig{}, fmt.Errorf("PULSE_UNRAID_CA_FILE requires a configured Unraid source and an absolute path")
		}
	}
	rows, err := intOrDefault("PULSE_AGENT_MAX_PROCESSES", 0, 1, maximumConfigurableRowCount)
	if err != nil {
		return AgentConfig{}, err
	}
	agent.MaxProcesses = rows
	return agent, nil
}

func durationOrDefault(key string, fallback, minimum, maximum time.Duration) (time.Duration, error) {
	raw := os.Getenv(key)
	if raw == "" {
		return fallback, nil
	}
	value, err := time.ParseDuration(raw)
	if err != nil || value < minimum || value > maximum {
		return 0, fmt.Errorf("%s must be a duration between %s and %s", key, minimum, maximum)
	}
	return value, nil
}

func intOrDefault(key string, fallback, minimum, maximum int) (int, error) {
	raw := os.Getenv(key)
	if raw == "" {
		return fallback, nil
	}
	value, err := parseInt(raw)
	if err != nil || value < minimum || value > maximum {
		return 0, fmt.Errorf("%s must be an integer between %d and %d", key, minimum, maximum)
	}
	return value, nil
}